Oily sludge degradation study under arid conditions using a combination of landfarm and bioreactor technologies

Hejazi, Ramzi Fouad (2002) Oily sludge degradation study under arid conditions using a combination of landfarm and bioreactor technologies. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Landfarming is one of the disposal methods used by oil companies to dispose of their generated oily sludge. Once in the soil, the sludge is subjected to biodegradation, leaching, and volatilization. Scientific studies to understand the degradation processes and to determine the degradation rate constants were mainly conducted in North American and European laboratories. However, no field studies were conducted in an arid region such as Saudi Arabia, the largest oil producer, where more than 30.000 m³ of oily sludge is generated annually. -- Field-scale research was conducted in the Juaymah area in the Eastern Province of Saudi Arabia to study the degradation of petroleum hydrocarbons under natural and enhanced conditions using landfarm and bioreactor technologies. The site was selected on the basis of its geographical location, site hydrology and climatic conditions. Based on factorial analysis, six landfarm and three bioreactor cells (2m x 2m) were designed, constructed, and operated for one year starting September 2000 using sludge from an Arab Medium crude tank bottom. Sampling was carried out on a monthly basis and the analysis conducted at Saudi Aramco laboratories following the US EPA (United States Environmental Protection Agency) standard methods. The studied parameters included: O&G (Oil and Grease), total hydrocarbon. BTEX (Benzene, Toluene, Ethyl benzene, and Xylene), pH, n-alkanes, microorganisms, metals, nutrients, and moisture content. -- The results of this study revealed that weathering (evaporation) and not biodegradation was the dominant degradation mechanism. Of the three operating parameters (tilling, addition of water and/or addition of nutrients), tilling was the main parameter responsible for the highest percentage of reduction (76%) in the O&G concentrations. The addition of nutrients and water changed the soil properties and hence minimized the weathering effect. As demonstrated by the C₁₇/Pr and C₁₈/Ph ratios obtained from the GC-FID analysis, only those cells, which received nutrients showed evidence for biodegradation. In addition, a novel bacterial species known as Burkholderia glumae was identified, for the first time in Saudi Arabia, as one of the indigenous soil microorganisms responsible for the biodegradation. -- The new analytical method of Open System Pyrolysis was used for the first time in this study and was compared with the routine O&G method to monitor oily sludge degradation. Although the results showed a similarity between these methods, however the Open System Pyrolysis provided a rapid method for the analysis of light volatile hydrocarbons in addition to several advantages over the O&G method. -- A new model was developed to reflect a mirror image of the S-shaped curve of the collected data. The results obtained from this model exhibited a better fit (R²) than the zero-order, first-order and Monod kinetics models. The two-level factorial analysis (2k) was used for the first time in this study to evaluate the significance of tilling, water, and nutrients to the overall degradation process. -- The analytical results revealed that due to the method of air addition, the bioreactor system was not effective in achieving a high percentage of O&G reduction. The O&G reduction data indicates that natural attenuation should not be used as an on-going treatment/disposal method for oily sludges mainly because it is a very slow process. -- The risk assessment revealed that landfarm activities pose a serious onsite risk particularly at the initial three-months loading period because of the presence of carcinogenic compounds such as benzene. -- Recommendations for future research direction in the area of degradation under arid conditions are included in the thesis.

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